/* 
enter的两个是进入时的两个形态变化
leave的两个是离开时的两个形态变化
页面过渡指令的name属性-enter-active
页面过渡指令的name属性-leave-active
页面过渡指令的name属性-enter
页面过渡指令的name属性-leave-to

*/
.modify-enter-active,
.modify-leave-active {
  transition: opacity 2s;
}
.modify-enter, 
.modify-leave-to /* .fade-leave-active below version 2.1.8 */ {
  opacity: 0;
}
